Because of the shrinking feature sizes in semiconductor wafers, greater degrees of precision are required in the stages used to provide the necessary motions. Because air-bearing stages allow for higher precision, they are commonly used to pattern and inspect semiconductor wafers. A point has been reached where optical techniques are limiting because of the width of the wavelength of light. Deep UV and even EUV processing will be required because of their shorter wavelength. The same or higher degree of precision is required in these processes, but they also require a vacuum environment. There are technical difficulties in attempting to use air-bearing stages in vacuum, as the escaping air increases the pressure in the vacuum chamber.
Many techniques have been employed to effect motion inside a vacuum chamber. Use of rolling element or plane bearing technology has been used but it is difficult to achieve the required precision. Air bearing systems with differentially pumped scavenge grooves have been employed inside a vacuum chamber. The difficulty here is that the stages quickly become very large to provide the required travels, necessitating large vacuum chambers, and because there is so much scavenging groove perimeter, it is difficult to achieve the low pressures required in the chamber. Another complicating factor in both these methods is that drives, encoders and services all have to be contained inside the vacuum chamber, causing problems with particulation and out gassing.
Methods to keep the mechanization outside of the vacuum chamber have been employed. These include linear and rotary contact seals, rotary ferro fluidic seals, expanding and contracting bellows. Also air bearings structures separated from the vacuum chamber by integral differentially pumped grooves that support some sort of a moving member through an aperture in the vacuum chamber wall. (Note U.S. Pat. No. 4,726,689 February 1988 Pollock, Varian; U.S. Pat. No. 5,898,179 April 1999 Smick, Applied Materials; U.S. Pat. No. 6,515,288 February 2003 Ryding, Applied Materials) have been tried and are the current state of the art in ion implantation. However, the above-noted problems with the prior art have not been successfully overcome.
The above-cited US 2006/0060259 A1 will be summarized. The disclosure in that application is somewhat similar to that of the present application and is summarized here for background information. Features of the devices and methods disclosed in the parent application can be incorporated into the present invention as appropriate.
FIG. 1a is a side view sectional schematic of a vacuum chamber stage 100 used for precision positioning of the semiconductor wafer or substrate 103 while the substrate is maintained in a vacuum chamber 117. The object of the apparatus is to expose the substrate to some sort of a manufacturing, processing or inspection for the purpose of manufacturing microelectronics circuits there on. Typically the substrate is exposed to some sort of radiation; examples of the many species of radiation would include but are not limited to Ions, x-rays, ultraviolet or extreme ultraviolet, electron beams, DUV (deep ultraviolet), extreme ultraviolet (soft x-rays) and visible light. Often this radiation needs to be conditioned by such devices as analyzers, magnets, mirrors or optics. This conditioning of radiation in this illustration is provided for in the area indicated by 119. This conditioning assembly is connected directly to the base reference member 104 with its output aperture 118 aligned with a consummate aperture 101 in the first reference plate 104.
Vacuum ports 225 for high vacuum conductance can be arrayed around the aperture 202 and connected on the opposite side of the base reference plate 206 to a manifold 203 connected to a cryopump or other low-pressure device. This arrangement allows for excellent conductance of pressure away from the area of interest. The ports may breakthrough into the wall of the aperture as in 102, or they may be completely through base reference plate 206 and arrayed around the aperture 202, as in FIG. 2a. Alternatively, or in addition, ports 102 could be used for directing radiation on an angle rather than normal to the surface of the substrate 103 with appropriate detectors arranged as needed, as for example is often the case in thin film measuring (ex. scatterometry and ellipsometry). The first reference plate 104 may be made from hard coated or nickel coated aluminum, nickel coated steel or stainless steel. Other materials such as ceramics or carbon fiber could also be considered. Important considerations are that the material be vacuum compatible, and the undersurface 106 may be made suitably flat to be used as an air bearing surface, and that the material have the structural strength to withstand the significant atmospheric pressures that may be applied to it without experiencing unaccepted distortions. The first reference plate 104 is shown as a simple plate for simplicity. It could easily be designed with structural ribs on the back; these ribs could also couple to additional mounting points for the radiation conditioning device providing a stiffer, firmer mount than the flange mount shown for simplicity. Avoiding distortions from atmospheric pressures is not a trivial issue; thousands of pounds of force will be equally distributed across a face of the vacuum chamber which will move around on the base reference plate. It is important that the reference base plate 104 remain flat because the smaller the air gap that can be used in the air bearing without contact the more efficient the lands between the differentially pumped grooves become. Engineering techniques for calculating and modeling these forces, including finite element analysis, are well-known in the art and need not be repeated here.
The vacuum chamber stage 114 with air bearing 115 and differentially vacuum pumped grooves 116 is urged against the lower surface 106 of the first reference plate 104 by thousands of pounds of atmospheric pressure. As air bearing surfaces 115 on the vacuum chamber stage 114 come within a thousandth of an inch of the reference base plate surface 106, pressure builds up in the gap 156 between them until equilibrium is reached. The stage then rides on this pressurized film of air, using atmospheric pressure as a preload force to create a very stiff, well damped air bearing free to translate in X, Y and theta. As with the first reference base plate 104, it is important that the vacuum chamber stage 114 have the requisite stiffness not to deform from the thousands of pounds of atmospheric pressure urging it toward the reference plate 104. The air bearing surface 115 in this preferred embodiment employs porous media compensation. Other air bearing compensation may be employed including but not limited to orifice and step compensation. Air bearings are a widely accepted art, much has been written about orifice and porous type air bearings, for porous media air bearings (see FIG. 1b). Porous media air bearings are most commonly made from porous carbon or graphite but may be made from porous alumina or silicon carbide. Carbon and graphite have excellent crash resistance and are very tolerant of inadvertent bearing face contact. Differentially pumped grooves are also well known in the art and are illustrated in FIG. 1b. Notice that in this preferred embodiment the grooves get wider and deeper progressively with lower air pressures. This is consistent with minimizing restriction and maximizing conductance of pressure away from the air bearing land areas.
This embodiment can be arranged so as to make it relatively simple to get a wafer 103 in and out of the vacuum chamber stage 114. A 25 mm×325 mm aperture 105 can be arranged in the side of a vacuum chamber stage 114, the vacuum chamber stage 114 can be physically docked against the load-unload station 107 see FIGS. 1c and 2c for the passing of wafers 103 in and out of the chamber without the introduction of atmospheric pressure to the chamber. Commercially available, but not shown, vacuum gates will be required.
By allowing for X and Y motions in a single plane it becomes convenient to use reference mirrors in the plane of the wafer and to drive the vacuum chamber stage through its center of mass. It is also possible to use reaction masses and service stages to improve the stage performance.
It is not necessary but it would be wise to provide another mechanism to urge the vacuum chamber stage 114 against the first reference plate 104. In the event that the vacuum chamber stage 114 loses the vacuum in the chamber 117, gravity would separate the vacuum chamber stage 114 from the first reference plate 106. This would result in a temporary unrecoverable situation. To avoid this situation, air bearings 111 acting upon a second reference plate or base 110 can be employed to urge the vacuum chamber stage 114 against the first reference plate 104 through a constant force springs mechanism 112.
The chuck 109 may be an electrostatic chuck or another chuck technology appropriate for vacuum. The chuck 109 may be mounted on a Z actuator or lifter mechanism 108 for the purpose of raising or lowering the substrate 103 in the VCS, for instance to facilitate substrate changes or to achieve a depth of field adjustment or fine planerization of the substrate. Many techniques known in the art are possible including piezos, super Z's, flexures or other mechanical lifters.
FIG. 2a shows a side view sectional view of a second preferred embodiment. This embodiment allows for the VCS 210 to contain an isolated vacuum chamber 223 as before but also operate in a vacuum 207. This can be a important feature minimizing problems which could occur regarding water vapor adhering to the first 222 or second 216 reference surfaces while the VCS is not over that area. This is accomplished by repeating the air bearing 214 and differentially pumped grooves 211 on the underside of the vacuum chamber stage 210. This is essentially two opposed mirror images.
A radiation source 201 can have a high conductance manifold 203 arrayed around the interface with the base reference plate 206. This manifold is attached to a vacuum pump via large aperture tube 204. Ports 225 through the first reference plate 206 surround the area of interest for good conduction, but are not necessary in all applications. The annular air bearing 214 is separated from the vacuum chamber 223 by differentially pumped grooves and seal lands 211 which are serviced by tubes from the motion system. This pattern is repeated exactly on the opposite side of the vacuum chamber stage 210. This second set of air bearing lands and differentially pumped grooves bear on surface 216 which is the top of the second reference plate 209. The opportunity exists to make the air bearing land area 214 smaller because in this embodiment the opposite pressures in the air bearing lands, grooves and chamber are exactly equal due to the fact that they are ported through common connections 217, 218, 220 and 221 to their source through 250, 251, 252 and 253. The pressurized air gaps 215 are preloaded against each other only. The air bearing 214 running on the second reference base 209 will be carrying the gravity load of the vacuum chamber stage 210 which would likely be 20 lbs. plus or minus an order of magnitude. The preload force between the bearings can easily be 10 times (one order of magnitude more than this gravity force), making the gravity force inconsequential. This allows the VCS to operate in a vacuum with the lowest pressure inside the VCS and isolated from contamination or pressure.
FIGS. 3a and 3b are sectional views of an X and Y vacuum chamber stage with rotation, and a differentially pumped port for transfer of the wafers or substrates and or high conductance pumping port, as in a third preferred embodiment.
Some applications, like thin film characterization, often employ rotation of the wafer. The embodiment of FIGS. 3a and 3b provides for rotation inside of an XY stage. By employing annular 360 degree radial air bearing surfaces isolated from the pass though by 360 degree radial differential pumped grooves and lands. As the XY stage is moved about, the radial bearings keep the rotating part centered. The XY stage carries a rotary actuator to spin the rotation part of the stage; it is possible to add an encoder. It is possible with differentially pumped grooves on outside of these bearings to operate the whole assembly in a vacuum environment. It will be necessary to vent the volume that the upper and lower 3 bearing set commonly leak into, it will also be necessary to vent the area under the rotating member to avoid pressure build up. An area 314 is provided for the motor and the encoder.
FIG. 4a, b, c show a device and method for ion implantation of substrates such a semiconductor wafers as in a fourth preferred embodiment. Ion implantation has moved from batch processing to serial processing. Serial processing provides more flexibility in the recipe that is administered to each wafer and more flexibility in the attitude of the wafer to the ion radiation, being able to pitch and rotate the wafer so as to dope or expose the sides of the via and the trenches equally. In order to keep throughput high, makers of ion implantation equipment have been migrating from spot or point beams that were scanned across the wafer in batch process to “ribbon” type beams. Ribbon type beams are slightly wider than the substrate or wafer being processed. The substrate may then be passed through the ribbon beam, exposing the whole substrate surface to the radiation. The beam may be a thin ribbon; 0.25 in, or a thick ribbon; 4 in. The thickness of the ribbon beam has an effect on the required travel of the wafer, which must pass though the entire ribbon before reversal.
FIG. 4a represents the preferred embodiment of the vacuum chamber stage device and method for modern ion implantation. The beam 409 in this case comes from below with the first reference plate 405 and vacuum chamber stage 403 nominally horizontal, although this could easily be reversed or at 45 degrees. The vacuum chamber stage 403, as in previous embodiments is urged against the opposite side 413 of the first reference plate 405 from the radiation source by atmospheric pressure
The vacuum chamber stage 403 is actuated by a motion system 417 outside of the vacuum area 402. The guidance for the motion system 418 could be from air bearings or rolling element bearings. In ion implantation motion characteristics are not as critical as in other precision applications and roller bearings would be an appropriate choice. The connection between the vacuum chamber stage 403 and the motion system 417 and actuators 418 could be with a blade flexure 450 which would decouple the vacuum chamber stage 403 from the drive and guide system in the Z direction which is constrained by the air bearing and atmospheric pressure against the vacuum chamber stage as in FIG. 4c. In this embodiment is not necessary to run vacuum services to the vacuum chamber stage 403. Because the motion on the vacuum chamber stage is linear only with respect to the base reference plate 405, holes or ports 415 through the first reference plate which aligned to the grooves 411 can be used to conduct pressure out of the grooves 411. Holes or ports 414 through the first reference plate 405 may also be used to conduct pressure from the chamber directly around the area of interest. These holes may be on an angle to clear the beam 409 during tilting. The chuck 406 holding the substrate or wafer 407 is mounted to a rotary actuator 401 through a Ferro fluidic, mechanical contact seal or air bearing with differentially pumped grooves. Continuous rotation is not required in this embodiment, only the ability to index 90 or 180 degrees, 90° in order to be able to get all the orthogonal groves and trenches, and 180 degrees in order to avoid tilting the plate in both directions as shown in FIG. 4b. Notice the whole reference plate may be tilted with respect to the Ion or radiation source. This tilting action, combined with a rotary motion allows complete coverage of all surfaces on the substrate including the sides of the via and trenches. This embodiment also allows for constant focus or distance from the Ion or radiation source providing the most uniform doping of the substrate.
Still further embodiments are possible, as will be described with reference to FIGS. 5a-5c. FIG. 5a shows two VCS's on reference members on opposite sides of a cylindrical member. One stage is a long travel and the other, a short travel high speed stage. FIG. 5b shows a VCS on a reference member incorporating components for writing and measuring a workpiece. FIG. 5c shows two VCS's on opposite sides of an opening in a single reference member.